The present disclosure relates to a method for braking of an internal combustion engine and a motor vehicle with a variable valve train for implementing the method.
Such a method is described by DE 39 22 884 A1, in which in the engine brake operation, besides the closing of a flap gate in the exhaust tract, a decompression effect significantly boosting the engine brake effect is achieved in that the outlet valves (inlet valves unchanged) are partly opened during each compression stroke by intervening in the valve controls of the internal combustion engine and in this way the air taken in during the intake stroke into the cylinder is decompressed by being blown into the exhaust tract. Moreover, the outlet valves are fully opened in normal operation during each exhaust stroke, i.e., with almost no decompression effect.
Examples of further methods for braking an internal combustion engine are disclosed in DE 10 2015 016 526 A1, DE 10 2005 033 163 A1, DE 196 49 174 A1 and U.S. Pat. No. 4,592,319 A.
Specifically, DE 10 2013 019 183 A1 discloses a method for controlling the engine brake effect of a valve-controlled internal combustion engine, especially a four-stroke internal combustion engine, for motor vehicles, wherein besides an exhaust gas accumulation in the exhaust gas line by closing a flap gate, a decompression effect is generated by partial, in particular irregular opening of at least one outlet valve per cylinder of the internal combustion engine. The at least one outlet valve is opened in the compression stroke and in the exhaust stroke, possibly with overlapping. In order to heighten the engine brake effect, the at least one outlet valve or at least one of the outlet valves is opened with a defined predetermined lesser valve stroke and/or one which is less than a regular valve stroke each time in the TDC region of the piston between the compression stroke and the expansion stroke and between the exhaust stroke and the intake stroke.
The potential drawback to the method known from DE 10 2013 019 183 A1 is that an unwanted engine excitation may occur at low engine speeds on account of the compressing of the gas in the exhaust stroke, for example when not all cylinders are being operated in the engine brake operation. This engine excitation may result in unwanted oscillations in the drive train.